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Дата изменения: Mon Jul 9 00:08:51 2007
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XMM-Newton Science Analysis System


selectlib (selectlib-4.69) [xmmsas_20070708_1801-7.1.0]

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Character string constants, operators and functions

Boolean subexpressions may also be formed from character string constants, identifiers that refer to text columns, and a limited set of associated operators and functions. As in C/C++ a string constant is a list of characters enclosed in double quotes ("). A double quote as part of the string must be preceded by a backslash. In addition, string constants may also be given as single-quoted text in which case they may contain un-escaped double quotes but no other single quote. Examples of valid string constants are: "XMM", "", "The double quote:$\backslash$"", 'A single-quoted string with a double quote (")'.

The following string operators and functions are available:

description	symbol/name	true example expression	comment
equality	==, !=	"X"=="X", "XMM"!="XTE"
relational operators	<, <=, >, >=	"a"<"b", "a"<="b",	lexicographical order
		"b">"a", "b">="a"
change case	upper/lower	upper("Xmm")=="XMM"
		lower("XMM")=="xmm"
length	strlen	strlen("XMM")==3,
		strlen("")==0
ASCII value	ascii	ascii(" ")==32,
		ascii("Z")-ascii("A")+1==26
concatenation	+	"Coca-"+"Cola"=="Coca-Cola"
range operator	[:], [:hi],	"XMM"[0:1]=="XM"	first character has index 0;
	[lo:], [lo:hi]	"FREDDY"[2:]=="EDDY"	omitted lower/upper bound
			expands to 0/actual length-1

Please note: The name of a string column can be used everywhere where a string constant is syntactically correct. An error condition will be raised if a numeric column is used in a textual context. All of the above string operators and functions can be arbitrarily nested to form more complex expressions, e.g. (upper(STRCOL1)[:3]+STRCOL2)[5:]==upper(STRCOL3).